Significant advances in recent years in the reduction in physical size and cost of electronic components have resulted from improvements in techniques for the manufacture of microelectronic circuits, e.g. microlithography. Microlithography, generally, comprises applying a film of a radiation-sensitive polymeric material, i.e. a resist medium, to one surface of a substrate, irradiating certain portions of the film with, e.g. with ultraviolet light, an electron beam, X-rays or the like, and developing the film with a solvent to remove the more soluble portions thereof. When positive resist is used, irradiation causes the resist medium to become more soluble in the developer solvent. The less soluble portion of the resist medium remaining on the surface of the substrate can then be employed as a protective mask to facilitate the selective etching or other treatment of the exposed portions of the substrate.
Etching of the substrate may be conventionally carried out by chemical treatment or by plasma discharge. Plasma etching, generally, affords finer resolution than chemical etching and is additionally advantageous in that it is free of the pollution and handling problems inherent in the use of chemical etchants. Many resist materials, however, cannot withstand plasma discharge and are eroded along with the substrate resulting in loss of pattern resolution. Therefore, chemical etching is more commonly used in spite of the above-named disadvantages. The present trend, however, is toward plasma etching because of its superior resolution, reproducibility, and throughput.
There is an ongoing search for materials that can withstand plasma etching without significant loss of resolution. Certain resists, for example, polystyrene and certain derivatives thereof, possess excellent resistance to plasma etching. These materials, however, are in almost every instance deficient to some degree in at least one of the other properties recognized as being essential for an acceptable recording medium.